Under the plans, the NCA will be tasked with pursuing serious criminals, including people-traffickers and drug-smugglers.

The proposals are set out in a restricted document obtained by this newspaper entitled Policing In The 21st Century.

They are expected to be announced in Parliament by Ms May tomorrow as part of a Police Reform and Social Responsibility Bill.

The document states: ‘Today’s organised criminals are nimble, entrepreneurial and no respecters of local, regional or national boundaries.

‘We will create a powerful new body of operational crime-fighters in the shape of a National Crime Agency, which will harness and exploit the intelligence, analytical and enforcement capabilities of the current law enforcement agencies.’

The NCA is expected to assimilate the Child Exploitation and Online Protection Centre and work closely with the UK Border Agency and HM Revenue & Customs. It will also take control of some specialist Metropolitan Police units, which have yet to be specified.

The document reveals that a Chief Constable, selected from one of the current police forces, will head the new team, and will report directly to the Home Secretary.

A source said: ‘The new force has been approved and has been designed specifically to become Britain’s very own FBI.

‘The overview used is to closely follow the American model, which is deemed to have worked well and can be mirrored by our own British team.’

The source also claimed that, for the first time, police officers working for the NCA will be referred to as agents.

Some observers say the powers of the NCA chief could well overshadow those enjoyed by Metropolitan Police Commissioner Sir Paul Stephenson.

A Home Office spokesman said: ‘It is our policy not to comment on leaked documents. We are due to announce to Parliament on Monday our plans to reform the police service.

‘The Government wants to ensure all aspects of policing are run effectively to tackle crime. This includes serious and organised crime, through strong links between local policing and work done beyond individual forces.’

The Home Secretary is also due to announce the introduction of so-called crime commissioners, who will be elected members of the public.

The leaked report says: ‘A single commissioner will be directly elected at the level of each force in England and Wales with the exception of the Metropolitan Police and the City of London Police.

‘They will represent and engage with the public, set local policing priorities, agree a local strategic plan, hold the Chief Constable to account, set the force budget and appoint the Chief Constable.’

Under the Government’s proposals, the Association of Chief Police Officers (ACPO) could be stripped of many of its responsibilities for overseeing counter-terrorism strategy, with these being handed to the NCA.

The move comes after The Mail on Sunday revealed how ACPO had amassed millions of pounds while being run as a private company.